Chinese engineers have blown up buildings in the town of Fengjie on the Yangtze River, beginning a new phase in the world's biggest water control project, the controversial Three Gorges dam reservoir. BBC News Online's Tom Housden outlines the project.

China's Three Gorges dam project to harness power from the Yangtze River is one of the most expensive and controversial engineering projects the world has ever seen.

When work on the three-stage scheme is completed in 2009, the 185-metre high dam will be the largest hydro-electric scheme in the world.

Officially the dam - which China's American embassy calls "a dream for generations to come true" - is expected to cost at least US$24bn.

Unofficial estimates say the project, which has been bedevilled by corruption and embezzlement, could cost at least three times this amount.

China hopes the dam will stop devastating floods

The dam is designed to generate electricity and reduce the risk of catastrophic flooding which has plagued the region for centuries.

But environmentalists have condemned the project for the devastating impact it is predicted to have on China's wildlife, eco-system and people.

The World Bank has refused to support the project because of these environmental concerns, while its design and construction standards have also been criticised by international experts.

Long-considered plan

The dam was originally the brainchild of the Chinese revolutionary hero Dr Sun Yat Sen, who came up with the idea of damming the Yangtze more than 80 years ago.

Some opponents believe the project should never have got off the drawing board

The plan was not seriously considered until the 1950s, when it was revived as part of Chairman Mao Zedong's Great Leap Forward.

However it was not until the 1990s that work began on the project under the guidance of former Prime Minister Li Peng.

The first stage, which lasted from 1994-97 consisted of diverting the Yangtze and starting to resettle people whose homes lay in the 600km-long (300 mile) area which will form the Three Gorges reservoir.

The next stage - due to be completed next year - will see the construction of the first batch of electricity generators, and the first permanent ship lock open for navigation.

The final phase will see the completion of the building of the hydro-electric generators. All 26 are expected to be on-line by 2009.

But as work has progressed, criticism of the dam has grown louder. Some opponents believe the project should never have got off the drawing board.

Serious flaws

Environmentalists point to what they say are serious flaws in a feasibility study conducted in 1978, which they believe failed to sufficiently convey the impact of the dam and exaggerated the benefits.

More than one million people are being resettled

Human rights groups have also condemned the resettlement plans, saying rural people have not been consulted, are often discriminated against, and are resettled on overcrowded, poor quality land.

China says 1.07 million people are being displaced, but critics say the figure is nearer 1.9 million.

Engineers have also expressed doubts over the project's entire feasibility, citing problems with sedimentation and the construction of the dam itself.

The latest concerns centre on fears that the reservoir will become severely polluted by sewage and rubbish from the city of Chongqing, which lies at its head.

In 1999, the city pumped about 1.3 billion tonnes of waste water into the Yangtze, of which more than 90% came from industrial sources.

Despite these issues, supporters of the project say the need for the dam is clear.

They point to the benefits of pollution-free hydro-electric energy, a lower risk of flooding downstream and improved navigation for shipping.